tcsh bug 1

tcsh finally has a feature that I requested back in the early '90s - they
call it "implicitcd." If you type a command and the command isn't found,
but it is a path to a directory, then it will cd you to that directory.
And it has a bug.
You can use environment variables to do this implicitcd as well, just
type the env var that points to a directory and you'll end up there.
tcsh also has the ability to do environment variable replacements, such as:

${some_var:s/foo/bar/}

But the replacement is done after the implicitcd check, so we can't use
replacements to implicitcd.
As an example, say we are in a directory that contains the path element
foo. And say there is another path that is identical except that it
contains the element bar.
We can do:

% cd ${cwd:s/foo/bar/}

But we can't do:

% ${cwd:s/foo/bar/}

Update: You also can't use implicitcd with the output of a command,
though I suppose this is a little more expected: